An 11-year-old boy shot and killed his grandmother before turning the gun on himself Saturday, the boy's grandfather told police in Arizona.

The Litchfield Park man told detectives that he and his 65-year-old wife "asked their grandson to clean his room and pick up after himself throughout the day, as he was being stubborn about it," Maricopa County Sheriff's Office spokesman Joaquin Enriquez said in a statement Sunday.

The couple then sat down on their living room couch to watch television, the grandfather told investigators.

"While doing so, the grandson came up behind them and shot (the grandmother) in the back of the head, with a handgun which belonged to the grandfather," Enriquez said.

The man told police that he ran after his grandson, but then returned to help his wife. He told detectives he heard another gunshot seconds later and saw his grandson take a few steps before collapsing from a self-inflicted wound.

The grandfather told sheriff's office investigators that he retrieved his gun and then called 911.

He told detectives that he and his wife had full custody of their grandson, the Maricopa County Sheriff's Office said.

'Nice family'

"In the preliminary stages of this investigation there had been no previous signs that the grandson might harm someone or himself and there was no cause for concern prior to this event," Enriquez said. "This is open ongoing investigation."

"Nice family. I knew the kid. I mean, he would ride his bicycle around, play around the neighborhood," Walter Venerable said. "It really hasn't set in just yet. I mean this is a nice neighborhood, it's really quiet -- as you can see -- it's just a tragic, tragic thing."

"It's just hard. You can't get your mind around it, you just can't," he said. "You have that neighborly connection but your heart just wishes that you had more and you could've done more, you could've seen something or said something."